I somehow made edit/object mode monochrome. How do I revert to default render settings?
I don't know if this is what you mean but you are in Texture display mode...see that little red and white checked ball to the right of the "Object Mode" dropdown?  Just hit 'Z' once to go to wireframe, or twice to go to Solid display mode...or click on that ball to choose a different rendering mode.  You probably hit Alt-Z instead of Ctrl-Z.